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PHOENIX  PHYSICAL  LABORATORY  CONTRIBUTIONS,  No. 


ON  THE  SPECTROSCOPIC  EXAMINATION  OF 
POSITIVE  RAYS  ISOLATED  BY  TRANS- 
MISSION   THROUGH    THIN 
PARTITIONS. 


BY 

ALFRED  NORTON  GOLDSMITH. 


SUBMITTED  IN  PARTIAL    FULFILLMENT  OF  THE  REQUIREMENTS 

FOR  THE  DEGREE  OF  DOCTOR  OF  PHILOSOPHY  IN 

THE    FACULTY    OF    PURE    SCIENCE, 

COLUMBIA  UNIVERSITY. 


1911. 


PHCENJX  PHYSICAL  LABORATORY  CONTRIBUTIONS,  No 


ON  THE  SPECTROSCOPIC   EXAMINATION   OF 
POSITIVE  RAYS  ISOLATED  BY  TRANS- 
MISSION   THROUGH    THIN 
PARTITIONS. 


BY 


ALFRED  NORTON  GOLDSMITH. 

M 


SUBMITTED  IN  PARTIAL    FULFILLMENT   OF  THE  REQUIREMENTS 

FOR  THE  DEGREE  OF  DOCTOR  OF  PHILOSOPHY  IN 

THE    FACULTY    OF    PURE    SCIENCE, 

COLUMBIA  UNIVERSITY. 


1911. 


ON  THE  SPECTROSCOPIC  EXAMINATION  OF  POSITIVE  RAYS 

ISOLATED    BY  TRANSMISSION    THROUGH 

THIN    PARTITIONS. 

BY     ALFRED     N.     GOLDSMITH. 

i.  INTRODUCTION. 

THlE  canal  rays  were  discovered  by  Goldstein  in  1886,  and 
through  the  researches  of  W.  Wien  in  1898,  and  later  of 
Sir  J.  J.  Thomson,  their  identity  with  the  positive  ions  was 
definitely  established.  They  have  been  frequently  employed  since 
as  a  source  of  positive  ions  for  investigation  of  the  properties  of 
positive  electricity. 

The  mode  of  production  of  the  canal  rays  involves  the  use  of  a 
perforated  cathode  in  a  tube  containing  a  gas  at  low  pressure 
through  which  an  electric  discharge  is  passing.  Back  of  the  per- 
foration in  the  cathode  will  be  found  a  column  of  rapidly  moving 
positive  ions,  their  presence  being  detectable  by  the  fluorescent, 
photographic  and  electrostatic  effects  which  they  can  produce.  J. 
Stark1  discovered  the  Doppler  effect  which  is  displayed  by  the 
canal  rays  behind  the  cathode,  as  evidenced  by  the  shift  of  the  lines 
of  the  spectrum  when  viewed  respectively  in  directions  perpendic- 
ular and  parallel  to  the  direction  of  motion  of  the  ions.  His  ex- 
periments showed  that  the  velocity  of  the  positive  ions  was  the 
same  as  the  velocity  of  the  ions  when  measured  by  means  of  the 
"magnetic  and  electric  spectra."  The  magnetic  and  electric  spec- 
tra are  obtained  when  the  ions  pass  through  strong  electric  and 
magnetic  fields.  From  the  observation  of  the  resulting  deflections 
of  the  beam  of  canal  rays  it  is  possible  to  evaluate  e/m  and  v. 

In  19x37  Thomson2  showed,  by  examination  of  the  magnetic  spec- 
trum obtained  in  gases  which  had  been  as  carefully  as  possible 
freed  from  all  traces  of  hydrogen  that  the  value  of  e/m  for  some 
of  the  positive  ions  was  (io)4,  5(io)3,  and  2.5(io)3.  The  two 
former  values  correspond  to  the  hydrogen  atom  and  molecule,  and 
the  latter  to  the  helium  atom.  At  lower  pressures  in  all  gases, 
positively  charged  atoms  of  hydrogen  were  found  to  be  present  in 
spite  of  the  attempts  at  purification  of  the  gas.  W.  Wien  then 


called  attention  to  his  earlier  hypotheses  that  the  positive  ions  lose 
their  positive  charge,  that  is,  are  neutralised  at  some  point  of  their 
path  and  then  may  be  again  positively  electrified  by  the  loss  of 
negative  electrons,  and  also  that  ions  of  larger  mass  than  those 
usually  found  exist  in  the  discharge.  His  conclusion3  that  the 
hydrogen  found  in  the  discharge  tube  was  present  only  as  an  im- 
purity was  disputed  by  J.  J.  Thomson4,  who  found  that  even  when 
the  amount  of  hydrogen  was  greatly  changed,  its  presence  did  not 
become  more  prominent.  He  suggested  later5  that,  reasoning  from 
the  constancy  of  the  velocity  of  the  canal  and  retrograde  rays,  they 
owe  their  velocity  either  to  an  explosion  in  the  atom  or  their  charge 
is  different  at  different  points  of  their  path.  Possibly  both  causes 
are  operative.  Wien's  hypothesis  of  the  existence  of  neutralised 
positive  ions  in  the  canal  rays  was  shown  to  be  well-founded  by 
experiments  undertaken  by  Thomson  in  icjoS.64  7 

W.  Wien  found8,  reasoning  from  the  experimentally  determined 
magnetic  deflections  of  the  positive  ions  in  the  canal  rays,  that  the 
greatest  velocity  they  attained  was  that  which  would  be  given  to  a 
positively  charged  atom  of  the  gas  which  owed  its  velocity  to  the 
potential  gradient  actually  existing  in  the  tube. 

As  early  as  1903,  J.  Stark9  had  suggested  that  neutral  doublets 
or  even  negatively  charged  canal  rays  might  be  produced,  and  that 
these,  moving  with  high  velocities,  would  cause  effects  similar  to 
those  produced  by  the  positive  ions. 

O.  Reichenheim10  showed  that  in  the  canal  rays  in  oxygen  there 
are  three  kinds  of  ions  prominently  present,  namely  the  hydrogen 
atom,  the  hydrogen  molecule,  and  the  oxygen  atom.  In  general 
the  spot  of  light  in  the  magnetic  spectrum  corresponding  to  the 
hydrogen  atom  is  the  most  evident.  Similarly,  the  presence  of  the 
hydrogen  atom  in  the  cases  where  the  tube  was  filled  with  argon  or 
nitrogen  was  observed,  though  in  these  cases  it  was  not  easy  to 
find  the  charged  atoms  of  the  gas  filling  the  tube. 

A  recent  research  of  Thomson11  established  the  existence  of  three 
kinds  of  canal  rays.  Firstly,  rays  which  are  not  deflected  by  elec- 
tric or  magnetic  forces.  Secondly,  "secondary  rays"  which  are 
produced  by  the  collision  of  rays  of  the  first  kind  with  the  mole- 
cules of  the  gas.  Thirdly,  rays  which  appear  at  low  pressures, 
have  velocities  proportional  to  the  difference  of  potential  between 
the  electrodes,  and  for  which  e/m  is  inversely  proportional  to  the 
atomic  weight  of  the  gas  in  the  tube.  The  secondary  rays  always 


have  a  velocity  of  2(io)8  cm.  per  second  and  a  value  of  e/m  of 
io4.  That  their  velocity  is  independent  of  the  potential  difference 
between  the  electrodes  suggests  that  they  may  be  produced  by  the 
dissociation  of  the  molecules  of  the  gas  by  a  sort  of  trigger  action, 
and  their  energy  comes  from  the  store  of  molecular  energy  origin- 
ally present. 

Certain  properties  of  the  a  rays  from  radium  are  of  interest 
and  will  be  briefly  considered.  Bragg  and  Kleeman12  first  dis- 
cussed the  diminution  of  velocity  of  the  a  particles  which  was 
sufficient  to  cause  them  to  lose  their  ionising  power.  They  found 
that  the  critical  velocity  was  about  i.5(io)9  cm.  per  second,  which 
is  60%  of  the  initial  velocity  of  the  homogeneous  rays  from  Ra- 
dium C.  It  is  quite  possible  that  uncharged  particles  not  electrically 
detectable  can  continue  passing  through  matter  even  at  the  end  of 
their  so-called  range,  for  it  is  a  very  improbable  assumption  that 
the  velocity  suddenly  falls  from  the  critical  value  to  zero. 

The  most  important  work  as  to  the  actual  nature  of  the  a.  rays 
was  done  by  Rutherford  and  Royds.13  By  passing  the  a  particles 
through  the  walls  of  a  thin  glass  chamber  (o.oi  mm.  thick)  into  a 
space  exhausted  to  a  high  vacuum  and  compressing  the  trapped  gas 
in  a  tube  where  its  spectrum  could  be  examined,  they  succeeded  in 
definitely  proving  that  the  a  particle  after  losing  its  positive 
charge  was  helium.  The  spectrum  of  the  helium  gradually  devel- 
oped in  the  spectrum  tube,  in  some  cases  taking  as  long  as  six  days 
to  become  completely  visible.  Check  experiments  were  performed 
to  test  for  possible  diffusion  or  leakage  of  the  gas  through  the  thin 
glass  containing  tube.  The  method  of  isolation  of  positive  rays  by 
transmission  through  thin  partitions,  so  successfully  employed  by 
Rutherford  in  this  instance,  was  used  in  the  present  research  into 
the  nature  of  the  canal  rays. 

II.  OBJECT  OF  THE  RESEARCH. 

The  following  experiments  are  an  attempt  to  pass  the  canal  rays 
through  a  thin  diaphragm  into  a  highly  vacuous  separate  chamber 
where  the  spectrum  of  the  accumulated  gas,  if  any,  can  be  ex- 
amined free  from  disturbances  of  the  electric  discharge  which 
produced  the  canal  rays. 


III.  DESCRIPTION  OF  THE  APPARATUS. 

The  discharge  tube  used  in  the  experiments  is  shown  in  figure  i. 
The  anode  is  A;  and  B,  a  ring  of  aluminum  with  a  large  hole  in 
its  center  is  the  cathode.  The  potentials  used  \vere  at  times  so  high 
that  it  was  difficult  to  secure  high  insulation  because  of  surface 
leakage  over  the  glass.  Therefore  the  terminal  wires  were  run 
from  the  platinum  leading-in  wires  at  6"  and  P  to  the  points  T  and 
Q  through  glass  tubes  which  were  sealed  in  place  and  of  which  the 
ends  were  filled  with  sealing  wax.  Connection  to  the  pumps  was 
secured  by  a  side  tube  at  F.  To  prevent  the  canal  rays  striking  the 
edge  of  the  disc  U  (where  the  sealing  cement  was  occasionally 
present)  a  guard  ring  was  placed  at  L. 


FIGURE  1. 


It  was  desirable  at  times  to  remove  the  plug  C  and  the  dia- 
phragm carried  therein  without  rebuilding  the  portion  of  the  ap- 
paratus surrounding  it,  and  this  became  possible  by  placing  a 
ground  joint  at  M.  The  thin  partition  used  in  the  experiments  was 
carried  on  the  front  face  of  the  steel  plug  C,  this  face  being  per- 
forated with  circular  holes  i  mm.  in  diameter.  The  thin  dia- 
phragm, through  which  the  canal  rays  passed,  was  sealed  with 


cement  on  the  front  face  of  C.  The  cement  was  very  carefully 
placed  so  that  none  of  it  was  in  the  path  of  the  moving  ions.  Over 
the  diaphragm  was  fastened  the  plate  U,  which  had  in  it  holes 
coinciding  in  size  and  position  with  those  in  V.  The  plate  U  was 
screwed  to  V  at  the  edges  after  cement  had  been  placed  on  the 
back  of  U  to  fasten  it  gas-tight  to  the  diaphragm.  As  before,  the 
cement  was  carefully  kept  out  of  the  path  of  the  ions.  The  steel 
plug  fits  into  place  at  N.  In  order  to  connect  that  portion  of  the 
apparatus  which  is  back  of  the  diaphragm  to  the  vacuum  pumps  an 
outlet  with  a  stop-cock  was  placed  at  K.  Connection  with  a  mer- 
cury reservoir  was  secured  through  the  tube  H ;  I  is  a  mercury- 
sealed  stop-cock  to  the  small  discharge  tube  E,  which  is  of  fairly 
fine  capillary  tubing.  Connected  to  E  is  G,  a  piece  of  the  finest 
capillary  tubing. 

It  will  be  seen  that  the  vacuum  apparatus  is  really  two  cham- 
bers, AB  and  CD,  which  are  divided  by  the  air-tight  partition  at 
U.  This  partition  was  thin  enough  to  permit  the  penetration  and 
passage  of  the  positive  rays.  These  particles  at  high  velocities 
were  thus  passed  from  the  chamber  AB  to  the  chamber  CD,  where 
they  accumulated  and  were  examined. 

Experiments  were  tried  in  air,  carbon  dioxid,  hydrogen,  argon, 
and  helium.  The  argon  was  prepared  by  sparking  air  in  the  pres- 
ence of  an  excess  of  oxygen,  which  excess  of  oxygen  was  after- 
ward removed  by  yellow  phosphorus.  Helium  was  produced  with 
the  same  apparatus  except  that  instead  of  starting  with  air,  the  gas 
obtained  by  heating  monazite  sand  was  used.  Since  this  gas  is  a 
mixture  of  air  and  helium,  it  was  not  difficult  to  secure  rapidly  the 
necessary  amount  of  helium. 

Gaede  and  Geryk  pumps  permitted  reaching  and  holding  a  vacu- 
um of  less  than  o.oooi  mm.  in  the  apparatus.  The  outlets  F  and  K 
were  so  arranged  that  either  portion  of  the  main  apparatus  or  both 
could  be  exhausted  at  will.  For  producing  the  discharge  in  AB, 
the  best  source  of  potential  was  found  to  be  a  large  static  machine, 
which  was  not  of  doubtful  or  changing  polarity  as  would  be  the 
case  with  an  induction  coil.  The  voltage  employed  was  determined 
by  the  use  of  an  auxiliary  spark  gap.  The  discharges  in  the  tube 
E  and  in  the  comparison  spectrum  tubes  were  produced  by  means 
of  a  small  induction  coil. 


IV.  CONSTRUCTION  AND  MANIPULATION. 

Much  difficulty  was  at  first  experienced  in  the  construction  of 
a  thin,  and  yet  gas-tight  diaphragm  at  U.  To  begin  with,  alum- 
inium foil  was  used.  It  was  found  that  the  best  imported  foil 
was  about  0.003  mm.  in  thickness  and  was  not  at  all  free  from 
holes.  Indeed  it  was  impossible  to  find  an  area  of  more  than  3  or 
4  square  mm.  which  did  not  have  a  hole  in  it.  The  thinnest  alum- 
inium foil  which  could  be  obtained  in  New  York  City  was  0.020 
mm.  thick,  and  quite  useless  because  of  the  immense  number  of 
holes  in  it. 

But  by  using  the  best  white  Indian  mica  and  carefully  splitting 
it  up  with  a  wedge  pointed  laparotomy  needle,  it  was  possible  to 
obtain  sheets  of  mica  of  the  required  dimensions  between  0.002 
and  0.006  mm.  thick,  and  free  from  all  visible  imperfections.  These 
sheets  of  mica  were  sealed  in  place  with  De  Khotinsky  cement 
which  was  sprinkled  carefully  over  the  sealing  metal  surfaces  in 
the  form  of  powder  and  then  melted  into  a  smooth  film,  thus  in- 
suring gas-tight  contact.  Both  the  front  and  rear  surfaces,  U  and 
V,  were  thus  treated  and  firmly  screwed  together  while  hot  with 
the  diaphragm  between  them. 

Careful  tests  repeated  many  times  established  the  fact  that  when 
the  pressure  on  one  side  of  the  diaphragm  was  o.oooi  mm.,  the 
pressure  on  the  other  side  might  be  2,000  times  as  much  without 
any  perceptible  leakage  occuring  in  intervals  of  an  hour  or  more. 

In  operation,  the  tube  AB  was  exhausted  to  a  pressure  of  a 
few  hundredths  of  a  mm.  or  less  and  the  portion  CKD  to  below 
o.oooi  mm.  The  discharge  in  AB  from  the  static  machine  was  then 
started.  In  order  to  eliminate  so  far  as  possible  the  foreign  gases 
occluded  in  the  electrodes  or  glass  of  the  main  tube,  the  discharge 
was  run  in  one  direction  for  some  hours  and  then  in  the  reversed 
direction  for  some  hours  with  the  pumps  working  all  the  time.  The 
capillary  discharge  tube  E  received  similar  treatment.  At  the  same 
time  the  air-tightness  of  the  diaphragm  was  tested. 

A  pink  fluorescence  at  certain  spots  of  the  tube,  accompanied  by 
considerable  heating,  was  at  times  observed.  This  phenomenon 
was  first  described  by  J.  E.  Lilienfeld14  and  explained  by  Gehrcke 
and  Reichenheim15,  who  showed  that  it  was  due  to  cathode  rays 
coming  from  secondary  cathodes  on  the  walls  of  the  tube. 


The  potential  in  the  main  tube  was  adjusted  by  altering  the  pres- 
sure therein.  On  running  a  discharge  through  E,  the  spectrum  of 
the  gas  which  had  accumulated  in  CKD  could  be  examined.  In 
order  to  get  a  bright  spectrum  with  only  small  quantities  of  gas 
present,  all  the  gas  in  D  was  compressed  to  several  thousand  times 
its  original  pressure  by  running  mercury  from  H  through  /  and  D 
to  /  and  then  shutting  the  cock  /.  A  brilliant  discharge  was  then 
obtained  in  E. 

For  a  time  the  mercury  lines  showed  uniformly  in  the  apparatus, 
and  it  was  thought  necessary  to  freeze  out  the  mercury  with  liquid 
air.  G  was  added  for  this  purpose.  It  proved,  however,  that  the 
improved  construction  which  was  then  adopted  with  a  stop-cock 
at  the  top  of  the  compression  reservoir  prevented  the  mercury 
from  volatilising,  because  the  cock  could  be  kept  shut  during  the 
discharge.  The  capillary  electrodes  were  never  permitted  to  come . 
into  contact  with  the  liquid  mercury  which  clings  to  them 
tenariously. 

A  preliminary  test  then  showed  that  after  putting  fresh  air  into 
the  apparatus,  running  the  main  tube  for  15  minutes  with  the  capil- 
lary portion  isolated,  and  compressing  the  gas  from  the  space  D 
into  E,  only  a  weak  air  spectrum  could  be  detected  in  the  capillary 
tube  E  when  a  discharge  was  passed  through  it. 

That  the  spectrum  of  the  gas  which  reaches  CKD  may  be  ex- 
pected to.be  visible  is  shown  by  the  following  roughly  approximate 
calculation.  Let  it  be  assumed  that  the  current  through  the  main 
discharge  tube  is  I,  and  that  the  fraction  i/R  of  the  current  carry- 
ing positive  ions  of  the  kind  finally  identified  in  the  capillary  com- 
pression chamber  pass  through  the  diaphragm.  These  may  not 
be  charged  atoms  of  the  gas  with  which  the  main  tube  has  been 
filled,  but  may  be  previously  occluded  hydrogen  atoms  which  have 
been  shot  through  the  diaphragm,  and  in  this  case  the  fraction 
i/R  may  become  quite  small.  On  the  other  hand,  if  the  charged 
atoms  of  the  gas  with  which  the  tube  is  filled  can  pass  through 
the  diaphragm,  i/R  will  be  much  larger.  Assume  also  that  a 
spectrum  can  be  observed  in  the  capillary  tube  when  the  pressure 
is  i/P  atmospheres. 

Let  that  portion  of  the  gas  in  CKD  which  is  trapped  in  the  com- 
pression chamber  be  i/n  of  the  whole,  and  let  the  volume  of  that 
chamber  be  V  cc.  When  the  gas  contained  therein  is  compressed 


8 

into  the  capillary,  let  the  compression  ratio  be  c:i.  The  charge  on 
an  ion  is  e. 

The  current  through  the  diaphragm  is  I/2R.  Thus  1/2  R  e  ions 
pass  through  the  diaphragm  per  second.  The  number  of  these 
which  reach  each  cc.  of  the  compression  bulb  after  t  seconds  is 
/  t/2  R  e  n  V .  When  these  are  compressed  into  the  capillary, 
there  will  be  present  in  each  cc.  /  t  c/ 2  Ren  V  ions  which  have 
become  neutralised  by  the  addition  of  negative  electrons,  that  is, 
molecules. 

If  under  normal  conditions  of  temperature,  there  are  N  mole- 
cules per  cc.  in  a  gas  at  atmospheric  pressure,  the  observation  of 
a  visible  spectrum  requires  that 

I  t  c  N 
—  — ,  and   therefore 


2  R  c  n  V         P 

2  R  c  n  V  N 


P  I  c 

The  following  are  estimated  and  approximate  values  of  the 
quantities  present  in  the  formula:  N  —  2.7 (io)19,  R  =  (io)6 
when  the  tube  is  filled  with  gases  other  than  those  finally  detected 
back  of  the  diaphragm,  or  R  =  (io)3  when  the  tube  is  filled  with  a 
gas  which  is  later  found  back  of  the  diaphragm,  e  =  4.9  (io)'10 
E.  S.  U.,  /  =  1.5  (io)6  E.  S.  U.,  n  =  3,  P  =  2.5  (io)5, 
c  =  5  (io)8,  V  =  loo. 

Depending  on  the  value  of  R  which  applies,  t  —  4,000  or  4  sec- 
onds. The  values  observed  were  one-half  and  ten  times  these 
calculated  quantities  respectively,  so  that  this  extremely  rough 
approximation  is  consistent  with  the  results  obtained. 

V.  EXPERIMENTS  IN  VARIOUS  GASES. 

The  actual  course  of  the  experiments  was  as  follows.  After 
taking  the  precautions  outlined  above  to  ensure  the  absence  of  any 
further  large  evolution  of  gas  from  the  electrodes  or  of  leakage 
through  the  diaphragm,  the  tube  was  run  steadily  at  nearly  con- 
stant voltage.  The  gas  in  the  capillary  tube  was  then  spectro- 
scopically  examined  after  compression,  and  showed  only  a  weak 
air  spectrum  due  to  un removed  air. 


With  the  main  tube  containing  air,  and  a  voltage  across  it  of 
35,000,  after  60  minutes  running  only  the  air  spectrum  of 
less  than  its  original  brightness  showed  in  the  capillary. 
After  90  minutes,  however,  a  weak  hydrogen  spectrum  showed 
which  steadily  became  more  brilliant  till  a  very  clear  and 
complete  hydrogen  spectrum  showed  after  150  minutes.  This 
spectrum  was  compared  line  for  line  with  various  standard 
spectrum  tubes  which  could  be  compared  with  each  other,  and 
the  identification  of  the  hydrogen  spectrum  was  complete.  On 
reducing  the  voltage  across  the  main  tube  to  25,000  by  increasing 
the  pressure,  120  minutes  were  required  to  show  a  weak  hydrogen 
spectrum ;  and  when  the  voltage  was  reduced  to  8,000  with  the  cor- 
responding rise  in  pressure,  no  hydrogen  spectrum  could  be  seen 
even  after  300  minutes. 

Carbon  dioxid,  carefully  freed  from  water  vapor,  was  then  sub- 
stituted for  air  in  the  apparatus.  With  a  voltage  of  28,000  the 
hydrogen  spectrum  showed  after  30  minutes,  and  as  before  the 
spectrum  became  stronger  with  time.  When  the  voltage  was  re- 
duced to  22,000,  60  minutes  wrere  required  for  a  visible  spectrum. 
And  with  a  voltage  of  6,000  only  an  extremely  doubtful  trace  of  a 
hydrogen  spectrum  was  observed  after  360  minutes. 

When  argon  was  placed  in  the  apparatus,  it  was  hard  to  get  a 
brilliant  discharge  through  the  main  tube  at  the  lower  pressures, 
and  the  fluorescence  was  comparatively  dim.  With  a  voltage  of 
40,000  after  120  minutes  a  faint  hydrogen  spectrum  was  found, 
which  spectrum  became  more  brilliant^  and  complete  after  con- 
tinued running.  When  the  voltage  was  34,000,  180  minutes  were 
needed  for  the  development  of  a  faint  hydrogen  spectrum.  A  pro- 
longed test,  wherein  the  tube  was  run  at  8,000  volts  for  over  400 
minutes  showed  no  hydrogen  spectrum. 

To  remove  all  traces  of  argon,  which,  as  several  investigators 
found,  clings  tenaciously  to  the  electrodes,  the  tube  was  washed 
out  repeatedly  with  air,  the  electrodes  being  approximately  freed 
from  occluded  gas  by  constant  powerful  discharges  through  the 
main  tube  and  the  capillary  portion. 

Helium  was  then  introduced.  As  before,  the  hydrogen  spectrum 
was  visible  after  60  minutes  running  when  the  discharge  voltage 
was  25,000,  and  120  minutes  sufficed  when  the  voltage  was  20,000. 
At  8,000  volts  it  was  believed  that  the  hydrogen  lines  could  be  very 
faintly  seen  after  300  minutes  running,  but  since  these  lines  re- 


10 

mained  extremely  dim  even  after  continued  running,  this  observa- 
tion was  regarded  as  of  little  weight. 

There  was  one  important  respect  in  which  helium  differed  from 
the  other  gases  examined,  namely,  that  while  the  hydrogen  spec- 
trum developed  in  time  in  the  capillary,  the  helium  spectrum  did 
the  same.  Attention  was  first  directed  to  this  point  by  the  bright- 
ness of  the  helium  lines  which  appeared  in  the  discharge  capillary 
with  the  hydrogen  lines  after  continued  running.  It  was  found 
that  both  hydrogen  and  helium  passed  through  the  diaphragm. 

From  the  nature  of  the  first  experiments,  since  the  apparatus  was 
in -any  case  filled  with  helium,  it  was  doubted  whether  this  observa- 
tion was  due  to  actual  passage  of  the  helium  through  the  diaphragm. 
To  test  this  point  further,  the  main  tube  was  filled  with  helium  at 
appropriate  pressure,  and  the  portion  CKD  was  washed  out  with 
air  and  then  pumped  to  a  low  pressure.  Thus  there  was  no  helium 
spectrum  obtained  from  the  capillary  discharge  tube  at  the  begin- 
ning of  the  experiment.  Experiment  then  showed  that  helium  did 
accumulate  in  the  capillary  at  what  was  estimated  as  more  than 
fifty  times  the  rate  of  accumulation  of  hydrogen.  The  helium 
passed  through  the  diaphragm  at  20,000  volts  and  probably  also 
at  considerably  lower  voltages. 

This  result  is  quite  explicable,  for  J.  J.  Thomson  found  that  in 
helium,  the  canal  rays  were  made  up  of  hydrogen  atoms,  hydro- 
gen molecules,  and  helium  atoms.  The  large  preponderance  of  the 
helium  atoms  in  the  discharge  tube  and  their  consequent  carriage 
of  the  greater  part  of  the  current  account  for  the  rapid  rate  at 
which  the  helium  passed  through  the  diaphragm. 

The  main  tube  was  then  filled  with  hydrogen,  and  the  capillary 
portion  with  air,  the  tube  and  electrodes  being  first  thoroughly 
cleaned  as  in  the  case  of  argon.  Experiment  showed  that  even 
with  so  low  a  voltage  as  10,000  and  300  seconds  for  the  discharge 
period,  the  hydrogen  spectrum  was  visible  in  the  capillary.  At 
higher  voltages,  the  time  was  more  than  proportionally  diminished. 

A  number  of  tests  were  made  to  determine  the  effect  of  a  mix- 
ture of  hydrogen  and  air  in  the  main  tube.  Mixtures  of  hydrogen 
and  air  in  known  proportions  were  therefore  placed  in  the  main 
tube,  and  air  alone  in  the  capillary  portion.  The  influence  of  the 
hydrogen  present  in  the  main  tube  on  the  time  of  appearance  of 
the  hydrogen  spectrum  was  very  marked.  Whereas  pure  air  in 


XI 

the  main  tube  yielded  at  25,000  volts  a  hydrogen  spectrum  in  the 
capillary  in  7,200  seconds,  0.1%  of  hydrogen  mixed  with  the  air 
reduced  this  time  to  900  seconds,  1.0%  of  hydrogen  to  200  sec- 
onds, 10%  of  hydrogen  to  100  seconds,  and  50%  or  more  of 
hydrogen  reduced  the  time  of  appearance  of  the  hydrogen  spec- 
trum to  practically  the  same  value  as  for  pure  hydrogen,  namely, 
60  seconds.  Similarly,  at  the  lower  voltage  of  10,000  pure  air 
showed  no  hydrogen  spectrum  in  the  capillary  after  18,000  seconds, 
and  0.1%  of  hydrogen  nothing  after  9,000  seconds,  yet  1.0%  of 
hydrogen  showed  the  hydrogen  spectrum  after  600  seconds,  and 
greater  percentages  of  hydrogen  acted  practically  the  same  as  pure 
hydrogen. 

Finally  a  test,  wherein  air  containing  i%  of  helium  was  used  in 
the  main  tube,  gave  a  result  quite  similar  to  that  described  above 
for  hydrogen.  That  is,  the  helium  spectrum  appeared  in  360  seconds 
as  against  90  seconds  for  the  case  where  the  discharge  tube  was 
filled  with  pure  helium.  However,  air  to  which  about  3%  of  argon 
was  added  showed  no  trace  of  argon  in  the  capillary  tube  even 
after  12,000  seconds,  so  that  clearly  the  argon  atoms  do  not  pass 
through  the  diaphragm  as  do  the  hydrogen  and  helium  atoms. 

To  ascertain  whether  the  retrograde  and  cathode  rays  would 
show  similar  effects,  the  polarity  of  the  electrodes  on  the  main 
tube  was  reversed  in  several  tests.  No  'hydrogen  or  helium 
spectrum  was  detected  at  any  time  under  these  circumstances. 
This  experiment  afforded  an  additional  proof  that  the  hydrogen 
i'ound  in  the  capillary  was  actually  due  to  the  canal  rays. 

In  the  above  experiments  attention  was  fixed  on  the  red  hydro- 
gen line  (C)  because  of  the  ease  with  which  it  can  be  identified. 
Its  position  was  found  from  a  standard  comparison  spectrum  tube 
at  the  time  of  observation  and  also  from  the  previously  calibrated 
scale  of  the  spectrometer.  Since  the  time  of  appearance  of  this 
line  depended  on  visual  acuity  and  sensitiveness,  that  is,  on  physio--- 
logical  factors,  not  any  great  accuracy  can  be  attached  to  the  num- 
erical estimates  of  the  time  of  first  appearance  of  the  spectrum. 
Experience  and  the  maintenance  of  nearly  constant  conditions  re- 
cuced  the  errors,  it  is  believed,  to  a  small  value. 

In  every  case  (except  for  the  lowest  voltage  used  with  each  gas) 
the  discharge  in  the  main  tube  was  continued  until  the  entire 


12 

spectrum  was  so  clear  and  unmistakable  as  to  check  perfectly  with 
the  comparison  spectrum  even  with  casual  visitors  observing. 
Traces  of  lines  not  checking  with  the  comparison  spectra  were 
carefully  searched  for,  but  no  unidentified  lines  were  found. 

VI.  ELECTRIC  AND  MAGNETIC  DEFLECTIONS. 

An  attempt  was  made  to  further  identify  the  moving  particles 
which  passed  through  the  diaphragm  by  obtaining  their  electric 
and  magnetic  spectra  by  the  method  of  Thomson  and  Wien.  In 
this  case,  all  the  holes  but  one  in  the  front  plate  U  were  blocked,  and 
a  fine  bore  tube  was  placed  back  of  this  hole.  The  apparatus  was 
so  arranged  that  the  beam  of  canal  rays  was  to  pass  through  a 
magnetic  field  of  known  strength  and  between  aluminium  plates 
maintained  at  a  known  difference  of  potential.  They  were  then 
to  strike  a  fine  grained  screen  of  willemite,  where  their  point  of  im- 
pact \vas  to  be  marked  by  a  bright  spot. 

The  following  calculation,  however,  made  it  questionable  whether 
the  particles  which  passed  through  the  diaphragm  would  have  a 
high  enough  velocity  to  produce  detectable  fluorescent  effects. 
Consider  the  hydrogen  atoms  which  pass  through  the  diaphragm. 
Imagine  that  these  ions  owe  their  entire  velocity  to  the  potential 
gradient  actually  existing  in  the  main  tube  through  which  they 
have  passed.  Let  m  be  the  mass  of  an  ion,  v  its  velocity,  V  the 
difference  of  potential  of  the  main  tube  electrodes,  and  e  the  charge 
of  the  ion.  Then 

1/2  m  vz=V  e. 

But  for  hydrogen  V  is  approximately  30,000  volts,  e/m=io*  E.  M. 
U.=3  (io)14  E.  S.  U.,  and  therefore  ^=2.5  (io)8  cm.  per  second. 
Similarly  the  value  for  the  helium  atom  is  ^-=1.7  (io)8  cm.  per 
second.  It  must  be  remembered  that  these  are  the  velocities  of  the 
ions  at  the  instant  that  they  strike  the  diaphragm ;  their  velocity 
after  passing  through  the  diaphragm  is  undoubtedly  much  lower. 
The  a  particle,  which  is  a  charged  helium  atom,  has  not  been  actually 
observed  to  produce  ionisation  (as  detected  through  fluorescence) 
at  lower  velocities  than  6  (io)8  cm.  per  second,  2J%  of  the  maxi- 
mum velocity.  But  it  is  quite  possible  and  even  highly  probable 
that  it  can  penetrate  matter  at  lower  velocities.  So  that,  though  the 
atoms  of  hydrogen  and  helium  pass  through  the  diaphragm,  their 


13 

passage  was  not  regarded  as  proof  that  they  might  be  expected  to 
show  a  bright  spot  on  the  willemite  screen. 

Another  possible  factor  in  the  production  of  fluorescence  must 
also  be  considered,  namely  that  the  fluorescence  may  be  dependent 
on  the  charge  carried  by  the  ion  as  well  as  on  its  velocity.  Thus, 
though  the  velocity  of  the  atoms  which  pass  through  the  diaphragm 
might  be  above  the  value  determined  by  J.  Stark16  to  be  necessary 
for  a  positive  ion  to  produce  fluorescence,  yet  the  neutralisation 
of  the  charge  of  the  ion  on  its  passage  through  the  diaphragm  might 
prevent  the  subsequent  appearance  of  fluorescence. 

A  considerable  number  of  experiments  with  air,  hydrogen,  and 
helium  showed  that  no  bright  spot  could  be  obtained.  The  pressure 
and  voltage  in  the  tube  were  varied  through  the  widest  attainable 
limits,  and  powerful  oscillatory  discharges  were  sent  through  the 
main  tube  as  well  as  the  unidirectional  discharges.  The  space  back 
of  the  diaphragm  was  pumped  to  the  lowest  vacua  so  that  the  pas- 
sage of  the  rays  would  not  be  impeded,  the  eye  of  the  observer 
was  specially  rested  to  secure  maximum  visual  sensitiveness,  and 
the  hole  through  which  the  ions  passed  had  its  dimensions  altered 
several  times.  Finally  the  original  diaphragm  was  replaced  by  one 
of  less  than  o.ooi  mm.  in  thickness.  In  no  case  could  any  definite 
bright  spot  be  detected. 


VII.  CONCLUSIONS. 

1.  Canal  rays  made  up  of  ions  of  hydrogen  or  helium  can  be 
given  sufficient  velocity  to  cause  them  to  pass  through  thin  material 
partitions. 

2.  When  the  discharge  tube  is  filled  with  air,  carbon  dioxid,  or 
argon  the  only  rays  that  pass  through  a  thin  partition  are  hydro- 
gen. 

3.  When  helium  is  used,  both  helium  and  hydrogen  atoms  pass 
through  the  partition,  the  helium  in  great  abundance. 

4.  When  hydrogen  is  used,  only  hydrogen  atoms  pass  through 
the  partition,  and  these  in  large  quantities. 

5.  The  atoms  which  pass  through  such  a  partition  are  not  capa- 
ble of  causing  fluorescence  on  screens. 

In  conclusion,  I  desire  to  express  rny  thanks  for  the  assistance 


14 

rendered  by  Professor  Bergen  Davis,  at  whose  suggestion  this  re- 
search was  undertaken,  and  who  has  frequently  placed  his  wide 
knowledge  of  the  subject  and  experience  in  experiment  at  my  dis- 
posal. 

PHCENIX  PHYSICAL  LABORATORIES, 

COLUMBIA  UNIVERSITY,  August,  1911. 


REFERENCES. 

1.  Phys.  Zeitschr.,  6,  p.  892,  1905. 

2.  Phil.  Mag.,  p.  561,  May,  1907. 

3.  Phil.  Mag.,  14,  p.  212,  1907. 

4.  Phil.  Mag.,  14,  p.  295,  1907. 

5.  Phil.  Mag.,  14,  p.  359,  1907. 

6.  Engineering,  85,  p.  518,  1908. 

7.  Phil.  Mag.,  16,  p.  657,  1908.  , 

8.  Ann.  d.  Physik,  <?/,  5,  p.  1025,  1908. 

9.  Phys.  Zeitschr.,  4,  p.  581,  1903. 

10.  Zeitschr.  Elektrotech.,  16,  pp.  583,  585,  1910. 

11.  Phil.  Mag.,  20,  p.  752,  1910. 

12.  Phil.  Mag.,  Dec.,  1904. 

13.  Chem.  News,  op,  p.  49,  1909. 

1.4.  Deutsch.  Phys.  Gesell.  Verh.,  8,  23  p.  631,  1906. 

15.  Deutsch.  Phys.  Gesell.  Verh.,  p,  21,  p.  593,  1907. 

16.  Ann.  d.  Physik,  21,  3,  p.  429,  1906. 


i6 


VITA. 

Alfred  Norton  Goldsmith  was  born  in  'New  York  City,  New 
York,  September  I5th,  1887.  In  1907  he  was  graduated  from 
the  College  of  the  City  of  New  York,  receiving  from  that  institu- 
tion the  degree  of  Bachelor  of  Sciences,  cum  laude.  He  was 
elected  to  membership  in  $  B  K  in  1907,  and  also  appointed 
to  a  Fellowship  at  the  College  of  the  City  of  New  York,  which 
Fellowship  he  held  till  1910.  During  the  years  of  1907  to  1911 
he  was  a  Graduate  Student  under  the  Faculty  of  Pure  Science  of 
Columbia  University.  Tutor  in  Physics  at  the  College  of  the 
City  of  New  York,  1911.  His  previous  publications  are 

"Elements  of  Physics,"  v  +  180  pages,  New  York,  1909. 

"Modern  Practise  in  Color  Photography,"  Columbia  School  of 
Mines  Quarterly,  Vol.  XXX,  Xo.  2. 

"Radiotelephony,"  Proceedings  of  the  Wireless  Institute,  Vol. 
1,  No.  6,  Nov.,  1909. 

And  several  shofter  monographs  in  allied  fields. 


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